title: Collateral ligament strains during knee joint laxity evaluation before and after TKA.
abstract: BACKGROUND
  Passive knee stability is provided by the soft tissue envelope. There is consensus among orthopedic surgeons that good outcome in Total Knee Arthroplasty requires equal tension in the medial/lateral compartment of the knee joint, as well as equal tension in the flexion/extension gap. The purpose of this study was to quantify the ligament laxity in the normal non-arthritic knee before and after Posterior-Stabilized Total Knee Arthroplasty. We hypothesized that the Medial/Lateral Collateral Ligament shows minimal changes in length when measured directly by extensometers in the native human knee during varus/valgus laxity testing. We also hypothesized that due to differences in material properties and surface geometry, native laxity is difficult to reconstruct using a Posterior-Stabilized Total Knee.
  
  
  METHODS
  Six specimens were used to perform this in vitro cadaver test using extensometers to provide numerical values for laxity and varus-valgus tilting in the frontal plane.
  
  
  RESULTS
  This study enabled a precise measurement of varus-valgus laxity as compared with the clinical assessment. The strains in both ligaments in the replaced knee were different from those in the native knee. Both ligaments were stretched in extension, in flexion the Medial Collateral Ligament tends to relax and the Lateral Collateral Ligament remains tight.
  
  
  CONCLUSIONS
  As material properties and surface geometry of the replaced knee add stiffness to the joint, we recommend to avoid overstuffing the joint, when using this type of Posterior-Stabilized Total Knee Arthroplasty, in order to obtain varus/valgus laxity close to the native joint.
authors.affiliation: Division of Biomechanics and Engineering Design, K.U. Leuven, Leuven, Belgium; Department of Orthopedics and Traumatology, K.U. Leuven, Leuven, Belgium. Electronic address: hendrik.delport@ortho-expert.be.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Delport
authors.forename: Luc
authors.initials: L
authors.lastname: Labey
authors.forename: Ronny
authors.initials: R
authors.lastname: De Corte
authors.forename: Bernardo
authors.initials: B
authors.lastname: Innocenti
authors.forename: Jos
authors.initials: J
authors.lastname: Vander Sloten
authors.forename: Johan
authors.initials: J
authors.lastname: Bellemans
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D017885:Collateral Ligaments / Q000503:physiopathology*; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery; D016059:Range of Motion, Articular; D013314:Stress, Mechanical
keywords: Laxity testing; Ligament strain; Posterior-stabilized prosthesis; Total Knee Arthroplasty